II. Decide which statement matches the text:

1. The radio pulse is fed directly into the aircraft which reflects it back.

2. The distance to the object is calculated from the time between the impulses propagated and reflected.

3. The more energy one puts into the pulse, the greater is the accuracy of time measurement.

4. The operating range of a radar is determined by two parametres: by the speed of the aircraft and by the wavelength of the impulse sent away.

III. Decide which statement does not match the text:

1. It is very simple to find the direction to the object: remember where you pointed the antenna.

2. One can make the pulse more powerful by making it longer.

3. The longer pulse increases the precision of time measurement.

4. The DPS system is equipped with a special filter to reduce the noise.

IV. Decide which definitions match the following terms:

1. propagate away a) distance at which a system works

2. radar b) a special device for concentrating a radio

impulse

3. operating range c) the system for radio location and ranging of the

object

4. directional antenna d) to transmit the energy impulse to the necessary

direction

V. Fill in the gaps with the words from the list below:

a radio transmitter, directional antenna, ranging, result in, compress

1. One of the most important parametres of any radar system is the accuracy and precision of _________________ .

2. It is not a problem to create a powerful source of energy, but only _________________ sends away a concentrated radio impulse.

3. A good efficient _________________ is the basic element of any radar system.

4. The ability of DSP _________________ the impulse _________________ the greater precision of ranging.

VI. Match the words in the right and left columns to make up a word expression from the text:

1. propagate a) measurement

2. directional b) in

3. time c) range

4. result d) site

5. transmission c) away

6. operating f) accuracy

7. reduce g) antenna

Computed Tomography

In 1895, Wilhelm Conrad Röntgen discovered that x-rays could pass through great amounts of matter. Medicine was revolutionized by the ability to look inside the living human body. Medical x-ray systems spread throughout the world in only a few years. In spite of its obvious success, medical x-ray imaging¹ was limited by four problems until Digital Signal Processing² appeared in the 1970s. First, overlapping³ structures in the body can hide behind each other. For example, portions of the heart might not be visible behind the ribs⁴. Second, it is not always possible to distinguish between similar tissues⁵. Third, x-ray images show anatomy, the body's structure, and not physiology, the body's operation. The x-ray image of a living person looks exactly like the x-ray image of a dead one! Fourth, x-ray exposure can cause cancer.

The problem of overlapping structures was solved in 1971 with the introduction of the first computed tomography. Computed tomography is a classic example of Digital Signal Processing. X-rays from many directions are passed through the section of the patient's body being examined. Instead of simply forming images with the detected x-rays, the signals are converted into digital data and stored in a computer. The information is then used to calculate images that appear to be slices⁶ through the body. These images show much greater detail than conventional techniques, allowing much better diagnosis and treatment. The impact of computed tomography was nearly as large as the original introduction of x-rays. Within only a few years, every major hospital in the world had access to computed tomography. In 1979, two of computed tomography' principle contributors, Godfrey N. Hounsfield and Allan M. Cormack, shared the Nobel Prize in Medicine.

The last three x-ray problems have been solved by using penetrating energy, such as radio and sound waves. Digital Signal Processing plays a key role in all these techniques. For example, Magnetic Resonance Imaging uses magnetic fields in conjunction⁷ with radio waves to probe the interior of the human body. (1780 p.s.)